Two studies comparing the use of manual chest compression vs. an automated chest compression device during resuscitation for out-of-hospital cardiac arrest produce contrasting findings, according to the studies in the June 14 issue of JAMA.

Out-of-hospital cardiac arrest claims hundreds of thousands of lives annually in North America. Successful resuscitation depends on a coordinated set of actions including early cardiopulmonary resuscitation (CPR), according to background information in the article. Observations of rescue personnel during CPR indicate that maintaining consistent chest compressions is a difficult task. The desire to provide optimal chest compressions led to the development of automated mechanical chest compression devices. The load-distributing band (LDB) is a circumferential chest compression device with an electrically activated constricting band on a short backboard and has been approved by the Food and Drug Administration for use in attempted resuscitation of cardiac arrest. Compared with manual chest compression, an automated LDB chest compression device produces greater blood flow to vital organs and may improve outcomes.

Al Hallstrom, Ph.D., of the University of Washington, Seattle, and colleagues conducted a study to compare LDB-CPR with manual CPR during out-of-hospital cardiac arrest. The multicenter, randomized trial included 1,071 patients who experienced out-of-hospital cardiac arrest in the United States and Canada. Patients received either standard emergency medical services (EMS) care for cardiac arrest with a LDB-CPR device (n = 554) or manual CPR (n = 517). The primary outcome measure included survival to 4 hours after the 911 call, with secondary measures being survival to hospital discharge and neurological status among survivors.

There was no significant difference in survival at 4 hours after the 911 call between the manual CPR group and the automated LDB-CPR group overall (29.5 percent vs. 28.5 percent) or among the primary study population (24.7 percent vs. 26.4 percent). Survival to hospital discharge was lower in the LDB-CPR group among primary episodes (5.8 percent vs. 9.9 percent), as was survival with intact neurological status.

"As implemented in this study, the use of an automated LDB-CPR device for resuscitation from out-of-hospital cardiac arrest appeared to result in lower survival and worse neurological outcomes than traditional manual CPR. Device design and implementation strategies may need further preclinical evaluation. The results of this study underscore the complexity of resuscitation from out-of-hospital cardiac arrest. Further work is required to understand the interaction of manual or assisted chest compressions with other aspects of resuscitation such as the phase of the arrest, drug choice and dose, timing of defibrillation, and treatments such as hypothermia and coronary reperfusion," the authors conclude.

Editor's Note: This study was sponsored by Revivant Corporation, now part of the ZOLL Corporation. Co-author Dr. Mosesso reported receiving equipment and supplies for the AED clinical trial from the ZOLL Corporation.

In another study, Marcus Eng Hock Ong, M.D., M.P.H., of Virginia Commonwealth University, Richmond, Va., and colleagues compared resuscitation outcomes before and after an urban EMS system switched from manual CPR to LDB CPR. The study included an analysis of 783 adults with out-of-hospital, nontraumatic cardiac arrest. A total of 499 patients were included in the manual CPR phase and 284 patients in the LDB-CPR phase. Of these patients, the LDB device was applied in 210 patients.

The researchers found that the rates of return of spontaneous circulation and survival to hospital admission were all significantly higher in the LDB-CPR phase, after adjustment for differences in EMS response time intervals and EMS witnessed. Survival to hospital discharge was higher in the LDB-CPR phase than in the manual CPR phase (9.7 percent vs. 2.9 percent), and was significantly higher after adjustment for differences in EMS response time intervals, EMS witnessed, and postresuscitation hypothermia, but there was no significant difference between the groups in terms of neurologic outcomes among survivors.

"In our study, OHCA clinical outcomes were improved following the introduction of LDB into an urban EMS system. The benefit was relatively robust across a range of patient subsets, especially for those patients with ventricular fibrillation initially, bystander witnessed events, and recipients of bystander CPR," the authors write.

"Our results suggest that a resuscitation strategy using the LDB CPR on rapidly responding EMS ambulances is associated with improved outcomes, including survival to hospital discharge, in adults with OHCA. These results suggest that the LDB device may be a useful addition to current cardiac arrest treatment options, especially when used early on patients with cardiac arrest who do not respond immediately to a brief period of manual CPR, defibrillation or both. However, further research (a large, adequately powered, prospective randomized clinical trial that blinds the rescuers to the intervention until they decide to initiate resuscitation) is needed to further define the value of LDB in resuscitation," the researcher conclude.

In an accompanying editorial, Roger J. Lewis, M.D., Ph.D., and James T. Niemann, M.D., of the Harbor-University of California Los Angeles Medical Center, Los Angeles, discuss the differences found in the studies comparing manual and automated chest compression for cardiac arrest.

"Can the differing conclusions of the 2 studies be reconciled? Although it is not possible to reach definitive conclusions until additional data are available, the best current information suggests that the degree of benefit or harm associated with use of the LDB-CPR device is influenced by the details of its use--perhaps including selection of the patient population with respect to presenting rhythm, time from cardiac arrest to initiation of CPR, and almost certainly time-to-deployment and the influence of deployment on time-to-defibrillation, when appropriate. To shed light on these questions, future comparative studies will need to pay particular attention to the definition and consistency of the method of use of the device, to measuring the multiple important time intervals with precision, and to ensuring the quality of the manual CPR administered in both trial groups."

"Conducting high-quality clinical trials in patients with out-of-hospital cardiac arrest is extremely difficult because of the complexity of EMS systems, strong preconceived notions regarding effective therapies, and the almost ubiquitous presence of unmeasured confounding factors that profoundly influence outcomes for individual patients and treatment effects. However, only by aggressively identifying and rigorously testing promising new therapies will the outcomes improve for patients who experience sudden cardiac death."